1. Field of the Invention
The present invention relates to a method and a device for generating a liquid mist for camouflage of, inter alia, ships, land vehicles, air vehicles and stationary objects, and as decoy within the infrared and radar wavelengths.
2. Description of the Related Art
It is known that mist, for instance water mist, can be used to camouflage an objector to produce decoys. If an object is covered by water mist, it will be difficult to discover by IR measurement and radar. By controlling temperature and/or size of droplets of the liquid used to generate the mist, it is possible to produce not only camouflage but also a mist which is an effective decoy for radar or IR homing devices.
Known devices for generating mist are using nozzles to atomise the liquid and spread the mist. Liquid under high pressure is used to produce the droplets that are necessary. Patent Specification EP 0 221 469 B discloses an example of a device for producing a decoy or camouflage by generating a mist. In this device, the mist is generated by means of water projectors provided with atomiser nozzles. The liquid is ejected intermittently through the nozzles. A drawback of intermittent spreading of mist is that there is a risk that a first layer of mist has time to drift away before the next layer has been positioned, which increases the risk of discovery.
German Patent Specification DE 37 06 781 A1 discloses a device for generating and spreading a continuous water mist, comprising a plurality of pairs of nozzles consisting of one nozzle for atomising of liquid and one nozzle arranged at an angle thereto and intended for compressed air. Water is ejected through the atomiser nozzle in the form of a layer of water droplets. This layer is hit by a flow of air from the compressed air nozzle, whereby the layer is spread and forms a mist.
Prior-art technique of generating mist by means of atomiser nozzles, however, suffers from several deficiencies. It takes quite a long time to produce a complete mist, thus requiring a long forewarning time in case of an attack by, for example, homing missiles. An atomiser nozzle generates mist having a predetermined droplet size. The droplet size is most important to the capability of the mist to camouflage an object. A mist intended to make an object invisible to an IR homing device gives poor protection against a radar homing device and vice versa. Therefore at least two types of atomiser nozzles are frequently used, one generating an IR mist and one generating a radar mist: a method requiring much space and making the device expensive. Moreover the device requires a water pressure of 250–300 bar to produce the desired size of droplets, which results not only in a high water and power consumption but also places great demands on pipes, connections and the like. In cold weather, there is also a risk of the atomiser nozzles being clogged by ice and the protected object being covered with ice. There is also a risk that the atomiser nozzles are clogged by dirt particles, especially in cases where the water used is lake water or sea water. This makes it necessary to include price increasing devices for filtering of water in the mist-generating device. Moreover, atomiser nozzles are poor at spreading the generated mist, which makes it necessary to use a plurality of nozzles to generate a sufficient layer of mist also for a small object. All in all, this results in a mist-generating device having a high water and power consumption and including a great number of large and heavy components.